1) Field of the Invention
The present invention relates to a power circuit that supplies a power source voltage to an image formation apparatus and a method of controlling a power source of an image formation apparatus.
2) Description of the Related Art
In recent years, there is a great demand to prevent the global warming for global environmental protection. In compliance with this requirement, serious considerations are given to conditions of energy saving, resource saving, and recycling at the time of operating and manufacturing various kinds of products. Among various conditions, the Energy Star proposed by the U.S. Environmental Protection Agency is introduced into Japan as an international power-saving prescription. In Japan, following the results of the conference on the prevention of global warming, Ministry of Economy, Trade and Industry (METI) announced a criterion of energy saving as the law concerning the Rational Use of Energy to be applied to specific devices such as copying machines, home electric appliances, and computers, and presented energy consumption efficiency targets in 2006.
The Energy Star is also reflected to the environmental regulations in the German Environmental Control BAM (Blue Angel Mark), the Nordic Swan Label, and the Swiss Energy 2000.
Based on a rapid spreading of image formation apparatuses into various fields in recent years, it is known that the waiting times of the image formation apparatuses such as printers and copying machines are longer than their operating times. Particularly, more than 90% of the time spent for printers of personal computers is said to be the waiting time. This started the prescription of the Energy Star.
In order to decrease unnecessary power consumption during the waiting time, an image formation apparatus disclosed in Japanese Patent Application Laid-Open No. 5-333636 proposes to use a switching-type power circuit for the power source of the image formation apparatus. This power circuit stops power supply to sections of the image formation apparatus that do not require power supply during the waiting time.
This type of conventional power circuit of an image formation apparatus is structured as shown in FIG. 6. A rectifier circuit 21 is connected to a first secondary winding 25a of a transformer 13, and a rectifier circuit 22 is connected to a second secondary winding 25b of a transformer 13. Driving output terminals td1 and td2 are provided as output terminals of the rectifier circuit 21 via a field-effect transistor (FET) 23. The field effect transistor 23 functions as a switching element. Driving sections that do not require a power supply during the waiting time such as a motor and a solenoid of the image formation apparatus not shown are connected to the driving output terminals td1 and td2. During the normal operation, a driving signal of 24-volts for driving the driving sections is output from the driving output terminals td1 and td2.
The rectifier circuit 22 is connected to the second secondary winding 25b of the transformer 13, as described above. Control output terminals tc1 and tc2 that output a control voltage of 5-volts to control circuits of a CPU (Central Processing Unit) and the like of the image formation apparatus are provided as output terminals of the rectifier circuit 22. A detecting circuit 10 that detects the output voltage is connected to the control output terminals tc1 and tc2.
A comparator circuit 11 that compares a detection voltage of the detecting circuit 10 with a preset reference voltage is connected to an output terminal of the detecting circuit 10. A pulse-width modulation (PWM) control circuit 18 that controls a pulse width modulation is connected to an output terminal of the comparator circuit 11. An output terminal of the pulse-width modulation control circuit 18 is connected to a gate of a field-effect transistor 8 that is insertion connected to a primary winding 24 of the transformer 13 as a switching element. An output terminal of an ON/OFF control circuit 15 is connected to a gate of the field-effect transistor 23.
In the power circuit having the above-described structure, the driving sections of the image formation apparatus are connected to the driving output terminals td1 and td2. The control circuits of a central processing unit (CPU) and the like of the image formation apparatus are connected to the control output terminals tc1 and tc2. When the driving voltage and the control voltage are supplied to the image formation apparatus, the image formation apparatus carries out an image formation operation in the normal operation mode.
In the normal operation mode, the field-effect transistor 23 is ON based on the output signal from the ON/OFF control circuit 15. When an alternating current (AC) voltage input through input terminals t1 and t2 is supplied to the primary winding 24 of the transformer 13, the rectifier circuit 21 rectifies a secondary voltage induced to the first secondary winding 25a of the transformer 13 so that a driving voltage of 24-volt, for example, is supplied to the image formation apparatus via the driving output terminals td1 and td2. Moreover, the rectifier circuit 22 rectifies a secondary voltage induced to the second secondary winding 25b of the transformer 13 so that a control voltage of 5-volt, for example, is supplied to the image formation apparatus via the control output terminals tc1 and tc2.
In the normal operation mode, the detecting circuit 10 detects the control voltages output to the control output terminals tc1 and tc2, and the comparator circuit 11 compares the detection voltages of the detecting circuit 10 with the reference voltage set in advance. Based on a result of the comparison, the pulse-width modulation control circuit 18 carries out a pulse-width modulation control in the primary winding 24 of the transformer 13 so that the control voltages from the control output terminals tc1 and tc2 become a predetermined voltage according to the control signal input to the gate of the field-effect transistor 8. Based on this pulse-width modulation control, the driving voltages output from the driving output terminals td1 and td2 are also controlled to become a predetermined voltage set in advance.
When a predetermined time set in advance elapses after the image formation apparatus ends the image formation in the normal operation mode, an energy saving signal F5 is generated based on the setting of the energy saving mode. This energy saving signal F5 is input to the ON/OFF control circuit 15. The field-effect transistor 23 becomes OFF based on the output signal from the ON/OFF control circuit 15, and interrupts the supply of the driving voltages to the driving sections that do not require power supply during the waiting time.
When a predetermined key operation is carried out or when there is an input of a printing signal, the setting of the operation mode returns from the energy saving mode to the normal operation mode. Based on the setting of the normal operation mode, the input of the energy saving signal F5 to the ON/OFF control circuit 15 is interrupted. Based on the output signal from the ON/OFF control circuit 15, the field-effect transistor 23 becomes ON, and the supply of the driving voltages from the driving output terminals td1 and td2 to the driving sections of the image formation apparatus is started. As a result, the image formation apparatus can carries out the image formation.
However, the driving sections of the motor and the solenoid of the image formation apparatus require at least 5 to 10 amperes. The field-effect transistor 8 is ON during both the normal operation mode and the energy saving mode, and the rectifier circuits 21 and 22 are ON during the normal operation mode. Therefore, the field-effect transistor 8 and the rectifier circuits 21 and 22 have substantially large power loss. Further, in order to restrict a rise in voltage when the driving output terminals td1 and td2 have no current load after ending the image formation operation, it is necessary to connect a dummy resistor R to the driving output terminals. Power consumption of the dummy resistor R lowers the energy saving efficiency during the waiting time of the image formation apparatus.